Signaling is taken to mean the exchange of signaling messages, for example between databases, switching nodes and terminals in a telecommunications network. A protocol for signaling is provided for example by signal system no. 7.
Signaling messages are needed for example for setting up, maintaining and releasing a telephone connection, transmitting call numbers, caller and call charge information, transmitting routing information for 0130, 0180 and 0190 numbers, extended functions such as call forwarding and conference calls, and the exchange of information between network operators on such things as the location of a mobile phone user.
The signaling network is often superimposed on the user data network, i.e. the transmission paths of the user channel in, for example, the TDM (Time Division Multiplex) method are used for physical transmission of the signaling messages; at higher levels, however, the networks are completely separate.
The signaling network contains signaling points (SP), with a distinction made between signal end points and signaling transfer points, and the transmission paths between the signaling points.
As regards the signaling end points, a distinction is made between service switching points (SSP) and service control points (SCP). A service switching point, for example, sends signaling messages to another service switching point that are needed for setting up, maintaining and releasing a telephone connection. A service switching point can also send a request to a database of a service control point in order, for example, to determine the routing information of a service call number (e.g. 0130 or 0800).
The connection between individual signaling points is handled via transmission sections, known as links. The individual signaling points are generally connected via multiple links.
The protocol structure of signaling system no. 7 consists essentially of the message transfer part (MTP) and the user parts (UP), with the message transfer part forming the transport system for the data of the user parts.
User parts for different applications include the ISUP (ISDN user part) and the TCAP (transaction capabilities application part).
The signal connection control part (SCCP) defined in the protocol structure adds certain functions to the message transfer part; typically it supports the transaction capabilities application part (TCAP).
The SCCP is used in the public switched telephone network (PSTN) and in the public land mobile telephone network (PLMN) for transporting signaling messages that are not assigned to any connection from a source to a destination, such as for database access in an intelligent network, callback on busy, mobile roaming, handover, etc.
The SCCP protocol is a protocol of signaling system no. 7 which has been standardized by the International Telecommunication Union (ITU) in Recommendations Q.711 to Q.714 and which performs some of the tasks of Layer 3 of the OSI model (Open Systems Interconnection); the SCCP protocol determines the routing of messages from a source to a destination.
For signaling messages that are not assigned to any connection, the users (user parts) of the SCCP use a general address that is globally valid, known as the global title, for identifying the destination. This global title address is a unique address within the transmission network and usually consists of a combination of digits (e.g. the dialed 0130 number or an identification number for a mobile phone user).
The general address (global title) is used by the relevant transfer node (STP) to determine further routing to the next signaling node (end node or transfer node) for translation. The general address is used by a global title translator (henceforth referred to as a processing device) for example for determining a destination (such as a further transfer node or an end node).
In accordance with prior art, the appropriate processing device that further processes the relevant signaling message performs this processing task for signaling messages according to destination information.
Routing may therefore take place on a static basis, i.e. by sending routing tables that contain the relevant destination information and very rarely change. Routing may also take place as a function of the loads on the appropriate transmission paths. In this case, routing based on the loads on the transmission paths is performed for each logical connection or for each individual signaling message.
Since the signaling network described also handles signaling for controlling user channels (e.g. telephone connections) the requirements that the signaling network has to meet in terms of quality of service (QoS), including security and real-time transmission, are high.
However this high quality of service is often not necessary for signaling messages, particularly if the signaling messages are ones that are not assigned to any connection. An example of such a message is a signaling message relating to SMS (short message service) traffic.
Signaling messages that relate to SMS traffic are transferred by the mobile application part (MAP) of signaling system no. 7. The MAP is an application part (user part) of signaling system no. 7 for signaling in mobile communication systems.
Routing for signaling messages according to prior art has the disadvantage however that all the signaling messages are transferred via the signaling network at a high quality of service. Expensive resources must therefore be provided for all types of signaling message, even if the type of message does not require this high quality of service.
Other features are linked with global title translation such as billing for the signaling and support for ported numbers, i.e. call numbers of subscribers who for example have moved house and have kept the number. Billing takes place according to the processing device used, i.e. according to the global title translator used for the relevant signaling message.
However, because the processing device is selected according to destination information, as already described, it is difficult for network operators to define different tariffs for billing different signaling messages.